1. Field of the Invention
The present invention relates to a solar cell, and a method for producing the solar cell.
2. Related Background Art
Thin-film solar cells using a thin-film semiconductor layer as a photo-absorber are under development in place of the bulk crystal silicon solar cells under spread of use. Among others, the thin-film solar cells using a p-type compound semiconductor layer containing a group Ib element, a group IIIb element, and a group VIb element, as a photo-absorbing layer are expected as next-generation solar cells because they show high energy conversion efficiencies and are unlikely to be deteriorated by light (cf. Japanese Patents No. 3249342, No. 3837114, and No. 3434259, Published Translation of PCT Application No. 2006-525671, Japanese Patents No. 3468328 and No. 3337494, Japanese Patent Application Laid-open No. 2004-047916, and Solar Energy Materials and Solar cells 67 (2001): 83-88). Specifically, the thin-film solar cells using as a photo-absorbing layer, CuInSe2 consisting of Cu, In, and Se (hereinafter “CIS”), or Cu(In1-a,Gaa)Se2 (hereinafter “CIGS”) obtained by replacing a part of In being the group IIIb element in CIS with Ga, demonstrate high conversion efficiencies (cf. Prog. Photovolt: Res. Appl. (2008), 16: 235-239).